1. Field of the Invention
The present invention relates to an apparatus for inspecting a structure including a heating tube, a tube sheet supporting the heating tube, and a flow distribution baffle, which are installed in a steam generator of a nuclear power plant, and for removing a foreign object, and more particularly, to an apparatus for visually inspecting and removing a foreign object in gaps of a bundle of heating tubes of an upper portion of a tube sheet of a secondary side of a steam generator, in which a detector is inserted into gaps of a bundle of heating tubes of an upper portion of a secondary side of a steam generator so as to inspect sludge or foreign objects, and a foreign object remover removes foreign objects when foreign objects are discovered in the gaps of the heating tubes.
2. Description of the Related Art
Generally, a steam generator is one of main facilities required to produce power from a steam turbine and a power generator in a nuclear power plant.
In detail, a plurality of heating tubes formed in a bundle are disposed in the steam generator. The heating tube performs as a heat exchanger between primary system water containing radioactivity and secondary system water turning a turbine, and separates the primary system water from the secondary system water.
Steam is generated as follows. The primary system water heated while passing through a nuclear reactor flows through a path in the heating tube of the steam generator. The secondary system water provided out of the heating tube contacts an external wall of the heating tube. Thus, heat exchange is performed between the primary system water and the secondary system water. The primary system water flows through the path of the heating tube, and circulates through the nuclear reactor. In addition, the secondary system water is changed to steam.
That is, radioactive water (i.e., the primary system water) with high temperature and pressure flows in the heating tube, and nonradioactive water (i.e., the secondary system water) flows out of the heating tube, wherein a wall of the heating tube is disposed between the primary system water and the secondary system water. Thus, if the heating tube is damaged, the radioactive water (i.e., the primary system water) flowing through the heating tube may be mixed with the nonradioactive water (i.e., the secondary system water) to be contaminated while leaking out of the heating tube, and thus radioactive contamination may occur throughout a space to which steam changed from the nonradioactive water (i.e., the secondary system water) is provided. Accordingly, it is most important to ensure reliability of heating tubes in various operations in a nuclear power plant.
FIG. 1 is a cross-sectional view of a conventional steam generator 10. FIG. 2A is a front cross-sectional view of the steam generator 10 of FIG. 1. FIG. 2B is a cross-sectional view for explaining a mechanism of the steam generator 10 of FIG. 1.
Referring to FIGS. 1, 2A and 2B, the steam generator 10 includes an inlet nozzle 1 into which a reactor coolant of a primary system flows, a heating tube 3 where heat exchange is performed, and an outlet nozzle 5 transferring heat from the reactor coolant flowing into the inlet nozzle 1 to a reactor coolant of a secondary system disposed out of the heating tube 3. The heating tube 3 is mounted on a tube sheet 4, and is supported by tube support plates 6 that are vertically arranged at predetermined intervals. A flow distribution baffle 8 shaped like a doughnut plate is installed between the lowest tube support plate 6 and the tube sheet 4 so as to support the heating tube 3. The heating tube 3, and the tube support plate 6 that are vertically arranged at predetermined intervals so as to support the heating tube 3 are coupled to a wrapper 20 of which a lower portion is opened and of which an upper portion has a steam outlet 21. Water is provided into the lower portion of the wrapper 20 along an inner wall of an external housing 2. The provided water generates steam by the heating tube 3, and then the steam is discharged upwards.
The steam generator 10 having the above-described structure generates heat as follows: the reactor coolant of the primary system flows through the inlet nozzle 1 in the heating tubes 3, passes through the outlet nozzle 5, and transfers heat to the reactor coolant of the secondary system disposed out of the heating tubes 3, thereby generating steam.
A portion of the steam generator 10 where a reactor coolant flows is referred to as a primary side, and a portion of the steam generator 10 where water is fed and steam flows is referred to as a secondary side. The secondary side of the steam generator 10 includes a main steam system, a turbine system, a condensate water system, and a feed-water system.
Thus, steam generated by the secondary side of the steam generator 10 moves through a main steam tube, and turns a turbine.
However, conventionally, when the steam generator 10 generates steam, although secondary water is filtered and chemically-treated so as to be provided to the secondary side, the secondary water accompanied with foreign objects and sludge which are generated due to various reasons while circulating in the heating tube 3 flows into the steam generator 10. Thus, the foreign objects and sludge may be deposited onto the tube sheet 4, the tube support plate 6, the flow distribution baffle 8, etc. or may be stuck to an external wall of the heating tube 3, thereby reducing heating efficiency of the steam generator 10 or damaging the steam generator 10.
That is, the steam generator 10 has a structure in which several thousands of U-shaped heating tubes 3 are disposed in a bundle type, both ends of the heating tube 3 are fixed to the tube sheet 4, and the heating tube 3 are supported by the tube support plates 6 that are vertically arranged so as to have seven steps at an interval of about 1 m up to an upper portion of the heating tube 3, as illustrated in FIG. 2. Impurities as scale generated due to various reasons when driving soft water flows are stuck to a surface of the heating tube 3, thereby reducing heat-exchange efficiencies. The impurities are deposited as sludge and are gradually solidified between the heating tube 3 and the tube support plate 6, and thus denting occurs between the tube support plate 6 and the heating tube 3, thereby damaging the heating tube 3. Accordingly, it is necessary to remove scale stuck to the surface of the heating tube 3 and sludge deposited on the tube support plate 6 in order to ensure efficiencies of the steam generator 10 and reliability of the heating tube 3.
To achieve this, a small-sized endoscope camera has been used to check states of the flow distribution baffle 8, the heating tube 3 and the tube sheet 4.
However, an operator needs to manually push the endoscope camera into a gap of a heating tube through a guide tube. Since the endoscope camera does not include an element for supporting the endoscope camera, the endoscope camera cannot find out and check a desired position. In addition, since a steam generator is surrounded by high radioactivity, an operator may be exposed to radioactivity, and therefore it is difficult to visually inspect or remove foreign objects.